The photoelectric process is an interaction between an X-ray photon and what?

• A. An inner shell electron
• B. A free proton
• C. An outer shell electron
• D. A nucleus

Answer: (A)

The photoelectric interaction happens when an X-ray photon is absorbed by a bound electron and all of the photon’s energy goes into releasing that electron from the atom. This is most likely with an inner-shell (K-shell) electron because those electrons are tightly bound and have binding energies that fall within the diagnostic X-ray range. When the photon energy exceeds the binding energy, the electron is ejected as a photoelectron, leaving a vacancy in the inner shell. The ejected electron’s kinetic energy is the difference between the incoming photon energy and the binding energy. The atom then de-excites, often emitting characteristic X-rays or Auger electrons.